REVENUE - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 914,890	$ 762,283
Gas
Disaggregation of Revenue [Line Items]
Revenue	907,728	752,980
Electric
Disaggregation of Revenue [Line Items]
Revenue	21	1,529
Solar
Disaggregation of Revenue [Line Items]
Revenue	1,016	1,911
Landfills
Disaggregation of Revenue [Line Items]
Revenue		425
Fuel Cells
Disaggregation of Revenue [Line Items]
Revenue	3,748	4,087
Other
Disaggregation of Revenue [Line Items]
Revenue	2,377	1,351
Residential
Disaggregation of Revenue [Line Items]
Revenue	326,793	273,005
Commercial & Industrial
Disaggregation of Revenue [Line Items]
Revenue	580,836	485,187
OSS & Capacity Release
Disaggregation of Revenue [Line Items]
Revenue	4,902	2,299
Other
Disaggregation of Revenue [Line Items]
Revenue	2,359	1,792
Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,393
SJG Utility Operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	292,432	229,962
SJG Utility Operations | Gas | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	292,432	229,962
SJG Utility Operations | Residential | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	208,728	166,589
SJG Utility Operations | Commercial & Industrial | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	77,889	60,313
SJG Utility Operations | OSS & Capacity Release | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	4,902	2,299
SJG Utility Operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	913	761
ETG Utility Operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	176,593	155,750
ETG Utility Operations | Gas | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	176,593	155,750
ETG Utility Operations | Residential | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	117,538	105,904
ETG Utility Operations | Commercial & Industrial | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	58,867	49,654
ETG Utility Operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	188	192
Wholesale Energy Operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	447,411	373,967
Wholesale Energy Operations | Gas | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	447,411	373,967
Wholesale Energy Operations | Commercial & Industrial | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	447,411	373,967
Retail Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,941	3,054
Retail Services | Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	21	1,607
Retail Services | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,920	1,447
Retail Services | Residential | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	527	512
Retail Services | Commercial & Industrial | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	21	1,607
Retail Services | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		935
Renewables | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	5,356	6,423
Renewables | Solar | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,016	1,911
Renewables | Landfills | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		425
Renewables | Fuel Cells | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	3,748	4,087
Renewables | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	592
Renewables | Commercial & Industrial | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	5,356	6,423
Corporate and Services | Intersegment
Disaggregation of Revenue [Line Items]
Revenue	(8,843)	(6,873)
Corporate and Services | Gas | Intersegment
Disaggregation of Revenue [Line Items]
Revenue	(8,708)	(6,699)
Corporate and Services | Electric | Intersegment
Disaggregation of Revenue [Line Items]
Revenue	0	(78)
Corporate and Services | Other | Intersegment
Disaggregation of Revenue [Line Items]
Revenue	(135)	(96)
Corporate and Services | Residential | Intersegment
Disaggregation of Revenue [Line Items]
Revenue	0
Corporate and Services | Commercial & Industrial | Intersegment
Disaggregation of Revenue [Line Items]
Revenue	(8,708)	(6,777)
Corporate and Services | Other | Intersegment
Disaggregation of Revenue [Line Items]
Revenue	$ (135)	$ (96)